Permanent magnet motors are utilized in applications such as hybrid and electric automobiles. Permanent magnet motors include a rotor having a core that supports permanent magnets and a stator that supports windings in proximity to the permanent magnets of the rotor. The interaction of the permanent magnet supported by the rotor core and the currents in the windings supported by the stator generate a rotary force for driving an automobile, as an example
The permanent magnets in the rotors are often skewed to reduce cogging and torque ripple in the permanent magnet motors. Skewing is the process by which the magnets in the rotor can be either placed an axial angle relative to one another or rotated in steps. The former process is called a continuous skew since the rotor magnet angle is continuously varied along the rotor length by placing the magnet in an angle. In the latter process, called the step skew, the machine rotor core is formed in portion along the machine axial length and the magnet of each portion is slightly rotated with respect to the magnet of the previous segment. Skewing reduces harmonics in the air-gap flux, and as a result, reduces the cogging and torque ripple. Cogging is the torque or force pulsation produced by the interaction of the rotating magnets with the stator teeth. Generally, torque ripple is a similar phenomenon to cogging, but affects the winding current. Skewing makes rotor manufacturing more complicated because the skewed magnets are more difficult to properly position and align. Evaluation of the permanent magnet motors and identification of incorrectly assembled rotors can be important, particularly at an end-of-line manufacturing test. Typically, the evaluation includes measuring the back electromotive force (EMF) generated in the windings of the stator by the rotating magnets of the rotor. However, the back EMF of an incorrectly assembled rotor may not vary sufficiently from that of a properly assembled rotor to signify an incorrect assembly of magnets.
Accordingly, it is desirable to provide improved methods for evaluating permanent magnet motors. In addition, it is desirable to provide improved systems for evaluating permanent magnet motors. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.